We present results of a search for giant radio galaxies (GRGs) with a projected largest linear size in excess of 1 Mpc. We designed a computational algorithm to identify contiguous emission regions, large and elongated enough to serve as GRG candidat
es, and applied it to the entire 1.4-GHz NRAO VLA Sky survey (NVSS). In a subsequent visual inspection of 1000 such regions we discovered 15 new GRGs, as well as many other candidate GRGs, some of them previously reported, for which no redshift was known. Our follow-up spectroscopy of 25 of the brighter hosts using two 2.1-m telescopes in Mexico, and four fainter hosts with the 10.4-m Gran Telescopio Canarias (GTC), yielded another 24 GRGs. We also obtained higher-resolution radio images with the Karl G. Jansky Very Large Array for GRG candidates with inconclusive radio structures in NVSS.
We present observations in the H53alpha line and radio continuum at 43 GHz carried out with the VLA in the D array (2 angular resolution) toward the starburst galaxy NGC 5253. VLA archival data have been reprocessed to produce a uniform set of 2, 1.3
and 0.7 cm high angular (0.2 X 0.1) radio continuum images. The RRL H53alpha, a previously reported measurement of the H92alpha RRL flux density and the reprocessed high angular resolution radio continuum flux densities have been modeled using a collection of HII regions. Based on the models, the ionized gas in the nuclear source has an electron density of ~6 X 10^4 cm^-3 and an volume filling factor of 0.05. A Lyman continuum photon production rate of 2 X 10^52 s^-1 is necessary to sustain the ionization in the nuclear region. The number of required O7 stars in the central 1.5 pc of the supernebula is ~ 2000. The H53alpha velocity gradient 10 km s^-1 arcsec^-1) implies a dynamical mass of ~3X10^5 Msun; this mass suggests the supernebula is confined by gravity.
